Metal‐Free Arylsulfonyl Radical Triggered Cascade Cyclization of Phenyl‐Linked 1,6‐Enynes: Synthesis of 2,3‐Dihydro‐1H‐indenes and 10a,11‐Dihydro‐10H‐benzo[b]fluorines

Abstract

Aryl sulfonyl radical triggered cascade cyclization of phenyl-linked 1,6-enynes for the synthesis of biologically important indenes containing alkenyl C-X bonds and 10a,11-dihydro-10H-benzo[b]fluorines is presented. In these radical cascade processes, three new chemical bonds, including C-

Recent Advances in Cyclization Reactions of 1,6‐Enynes

“…The subsequent radical In the same year, the Huang group disclosed a cascade cyclization of phenyl-linked 1,6-enynes with substituted sulfonyl hydrazides for the generation of biologically important indenes and 11-dihydro-10Hbenzo[b]fluorines in good to excellent yields (Scheme 119). [94] The arylsulfonyl radical-triggered protocol entailed the construction of CÀ S, CÀ C, and CÀ X bonds in one step by the NIS/TBHP promoteddesulfonylation reactions. This strategy features the advantages of metal-free, mild reaction conditions, broad substrate scope, and good functional group tolerance.…”

Persulfate promoted carbamoylation of N-arylacrylamides and N-arylcinnamamides with 4-carbamoyl-Hantzsch esters

“…According to the literature 5,10,11 and the above experiments, a plausible mechanism involving a radical process is proposed herein (Scheme 3). 4-Carbamoyl Hantzsch ester 1 is first oxidized by (NH 4 ) 2 S 2 O 8 , generating the carbamoyl radical A via a single electron transfer process.…”

Radical bicyclization of 1,6-enynes with sulfonyl hydrazides by the use of TBAI/TBHP in the aqueous phase

“…8 In recent years, the cyclization of 1, n -enynes with sulfonyl hydrazides has been extensively studied, with the pioneering works being dominated by three common models. 9 The first type is the sulfonylation of 1, n -enynes, where the sulfonyl radical-enabled regionoselectively attacks the CC or CC bond of 1, n -enynes in the oxidation system, and then the new radical intermediate is terminated after a single intramolecular cyclization (Scheme 1.1). 9 a – e The second type is the halosulfonylation of 1, n -enynes, where the sulfonyl radical is selectively added to the CC bond, followed by a single intramolecular cyclization with the CC bond to give the vinyl radical, which is eventually terminated by the reaction with the halogen (Scheme 1.2).…”

“…Herein, we design a mild TBAI-TBHP catalytic oxidation system running in the aqueous phase for the preparation of polyheterocycles via 5- exo-dig /6- endo-trig bicyclization of 1,6-enynes with sulfonyl hydrazides, while TBAI acts as both a radical initiator and a phase transfer catalyst in this transformation (Scheme 1.4). Notably, this is a novel bicyclization approach with a different reaction pathway from all the previous ones 9 and the iodosulfonylation products can be obtained by designing the structure of 1,6-enynes.…”